(a) Field of the Invention
The present invention relates to a preparation method of α-alumina nano powder, and more particularly to a preparation method of α-alumina nano powder which has uniform particle shape and size distribution, is capable of being produced at a low temperature, and contains less than 20 ppm of alkali metals such as Na and K.
(b) Description of the Related Art
In today's applied technology field, interest in nano technology, including nano particles, nano structure, and nano devices, is on the increase. Especially in the semiconductor industry, the need of a much finer linewidth of wires and multiple wiring is increasing with regard to super-integrated circuits.
The chemical-mechanical planarization (CMP) technique is an important high-level planarization technique that completely removes differences in wiring gaps of multiple circuits. In chemical-mechanical planarization, a chemically-treated surface is polished by mechanical movement of a slurry and a pad. The slurry used in the chemical-mechanical planarization refers to a solution wherein an abrasive with a dimension of tens to hundreds of nanometers is suspended in pure water. The abrasion rate and post-abrasion defects depend on the kind, size, and concentration of the abrasive.
α-Alumina has superior mechanical, electrical, and optical properties, and is widely used for abrasives, plasma sprays, fillers, sintering materials, fluorescent materials, insulators, optical materials, etc. In particular, α-alumina having a fine and uniform structure and narrow particle size distribution is required as a precision abrasive. The Bayer method makes mass production of α-alumina powder possible by converting bauxite to aluminum hydroxide or transition alumina and calcinating it in the air. However, α-alumina having superior crystallinity and purity cannot be obtained by this method. Also, due to the huge agglomeration of aluminum hydroxide or transition alumina, α-alumina powder tends to have a coarse and irregular particle structure. Moreover, a high temperature of about 1,230° C. is required for complete transition, since the degree of transition depends on temperature and time of heat treatment.
As solutions to these problems, research on solution-powder synthesis, such as the sol-gel method, hydrothermal method, and co-precipitation method, are actively in progress. The solution-powder synthesis method offers stoichiometric crystalline ceramic particles of good purity. In particular, the hydrothermal method is capable of growing single-crystal particles at a very much lower temperature and of controlling particle size and shape. Therefore, this method is widely being researched and commercially applied. The problem of α-alumina synthesis by the hydrothermal method is that it takes an excessive amount of time because of the high temperature and pressure that are required.
In this regard, research on synthesis using organic solvent instead of aqueous solution is being carried out. Adair, et al. synthesized α-alumina having a narrow particle size distribution using glycol, which is a secondary alcohol. Also, they could control particle size and shape by regulating the concentration of the nucleation seed and stirring rate. However, if aluminum hydroxide obtained from the precipitation method is used as a precursor, contamination by alkali metals such as Na and K is inevitable, and high-purity α-alumina cannot be obtained.
Accordingly, there is a need for a method for preparing high-purity α-alumina having a uniform particle shape and size distribution and that is safe from contamination by alkali metals such as Na and K.